Aqueous insecticidal pour-on formulation

ABSTRACT

A topically acceptable aqueous pour-on formulation adapted for localized external application to an animal, which format includes an effective amount of a water insoluble insect growth regulator (IGR), a suspending agent, a surfactant or mixture of surfactants, and an aqueous carrier.

This application is a 371 of PCT/AU98/01,046 filed Feb. 18, 1998.

FIELD OF THE INVENTION

The present invention relates to an aqueous pour-on formulation of waterinsoluble insect growth regulator (IGR), and a method of treatinganimals using this formulation.

BACKGROUND ART

Traditionally, animals have generally been treated for the control ofparasites, by either dipping the whole animal in a bath containing aparasiticidally effective agent or by spraying the entire body surfaceof the animal with such an agent. More recently, it has been found thata number of parasiticidally effective substances may be applied bylocalised application (so-called “pour-on” application). Although theparasiticidally effective substance is supplied by localisedapplication, the active agent migrates so as to protect the wholeexternal surface of the animal. By “localised application” it is meantthat the active ingredient is only applied to a minor portion of theouter surface of the animal, generally as a line or spot on the animal'sback.

Prior Art Formulations

(a) Non Aqueous Pour-On Formulations

Various pour-on formulations are described in Australian patent nos.560078, 563723, and 546672. In most pour-on formulations, and in allcurrent water insoluble IGR pour-on formulations known to the inventors,the active agent is dissolved in a non-aqueous solvent system to producea suitable pour-on formulation.

It has become apparent that non-aqueous pour-on formulations alsopossess a number of disadvantages. In particular, the formulation maypose handling problems caused by the flammability or toxicity of thesolvents, and lead to high tissue residue levels in animals treated withthe formulations.

Formulations based on water immiscible solvents would either run off wetanimals or be washed off by rainfall which occurred after treatment.

On contact with water, the active rapidly precipitates out ofnon-aqueous formulations which are based on water miscible solvents. Ifthis formulation is applied to a wet animal, or if the animal is exposedto rain before the treatment has dried on the animal, the activeprecipitates out of solution and is deposited along the back of theanimal, the solvents also being washed away by the rain. This hinders orprevents the spread of the active ingredient around the entire animal.This phenomenon is particularly important to those areas on theunderside of the animal. This reduces the effectiveness of solvent onlybased formulations under these conditions.

(b) Aqueous Dip Formulations

An aqueous dip formulation of IGR is also known.

However, such a dip formulation would not be suitable as a pour-onformulation in either the undiluted or diluted state for the followingreasons.

Undiluted Dip Formulation

This would not be satisfactory because:

(i) In order to deliver the same amount of active per animal, the dosevolume would be too small. That is, 2 mL would be applied to themajority of animals, which would be a major issue for accurate dosing byfarmers. A very small dose volume would be too localised to allowspreading to all parts of the animal as described above.

(ii) Due to the high levels of surfactants in an undiluted dipformulation, the presence of water, particularly high rainfall, wouldtend to wash the active off the animal.

Diluted Dip Formulation

This situation would arise where the above-mentioned dip formulation isdiluted to achieve what would be considered a satisfactory concentrationof active. However, this would not be satisfactory for the followingreasons:

(i) If the dip formulation were diluted in a backpack or drum, theactive would almost immediately commence to settle out of theformulation due to dilution of the suspending agent. This would createunder/over dosing as described above.

(ii) Because the sedimented active would no longer be associated withthe spreading/wetting agents, it would essentially be deposited alongthe line of application and have no means to disperse.

With regard to the possibility of aqueous pour-on formulations, andbased on non-aqueous pour-on formulations, it would be expected by thoseskilled in this art that aqueous pour-on formulations containing waterinsoluble IGRs would not be effective because of problems with spreadingand physical stability as follows.

Spreading

It has generally been believed that a non-aqueous solvent is required toboth dissolve the water insoluble IGR and help disperse the active sothat it reaches all parasites on the animal. Without such spreading, theactive would not reach all of the parasites, and would therefore beineffective. Such spreading, in particular with sheep, also involves themovement of the active into the greasy layer of the wool. This isfacilitated by the solvents which “push” the active into the layer whileat the same time providing the physical spreading described above.

Physical Stability

Because of the insolubility of the IGR in water, it is necessary to“suspend” the active in the formulation so that it does not settle onstanding. If such settling occurs to a significant degree, then it isdifficult to redisperse it to achieve an accurate dose rate forapplication to the animal. Thus, there is in effect a caking of theactive at the bottom of the container. This is a major reason why manyaqueous suspensions have problems. The result is that an animal treatedwith product from the upper part of the container is underdosed, whilean animal treated with the product from the lower part of the containeris overdosed. This may have fatal consequences.

Aqueous formulations of water insoluble IGRs are more accuratelydescribed as suspensions. It would be expected that when suchformulations are applied to animals as pour-ons, the suspended activewould remain at the site of application, thereby exacerbating thespreading problems described above. Furthermore, it has been shown thatwhen other water insoluble actives are applied to animals such as sheepin an aqueous pour-on formulation, the majority of the active grows outwith the wool staple, effectively being carried away from the skinsurface where it is needed to control the parasites.

DISCLOSURE OF THE INVENTION

It has now been surprisingly found that an aqueous based pour-onformulation containing a water insoluble insect growth regulator(IGR)and a blend of surfactant and wetting agents is efficacious incontrolling sheep lice. The formulation has the advantage overtraditional non-aqueous solvent based formulations because it israinfast and leads to very low pesticide tissue residue levels in theanimals after application.

A surprising demonstration of the efficacy of this pour-on formulationis that at concentrations of 12.5 and 25.0 g/L diflubenzuron, whenapplied as a 20 ml dose along the backline of sheep, 100% lice killswere reported within 20 weeks. The majority of lice (95%) were killedwithin 10 weeks of application with the rest being killed over theremainder of the 20 week period.

It has also surprisingly been found that adding the formulations of thisinvention to an already wet animal does not affect the efficacy of theformulation. Likewise, if it rains shortly after the formulations ofthis invention are applied, the speed of efficiency of the active isincreased compared to situations where no rainfall occurs aftertreatment. In both instances, it is believed that the surfactantspromote the spread of the active over the surface of the animal.

Thus, in a first aspect, the present invention provides a topicallyacceptable aqueous pour-on formulation adapted for localised externalapplication to an animal, which formulation includes an effective amountof a water insoluble insect growth regulator (IGR), a suspending agent,a surfactant or mixture of surfactants, and an aqueous carrier.

Because of the insolubility of IGR in water, it is necessary to suspendthe active in the formulation so it does not settle on standing.Accordingly, it is necessary to include in the formulation a sufficientamount of a suspending agent.

In a second aspect, the present invention provides a method forcontrolling external parasites on an animal which method includesexternally applying to an animal an effective amount of a aqueouspour-on formulation adapted for localised external application to ananimal, which formulation includes an effective amount of a waterinsoluble IGR, a suspending agent, a surfactant or mixture ofsurfactants, and an aqueous carrier.

Any water insoluble IGR could be used in the formulation according tothe present invention. Suitable IGRs include diflubenzuron, triflumuron,fluazuron, and methoprene. A particularly preferred IGR isdiflubenzuron. For the formulation to be effective, the IGR must besuspended in the aqueous carrier.

Suitable suspending agents include xanthan gum, colloidal silica,bentonite, polyvinyl pyrrolidone, cellulose derivatives and alginates.The particularly preferred suspending agent is xanthan gum.

Any anionic or nonionic surfactant could be used in this formulation. Apreferred anionic surfactant is alkylated naphthalene sulphonate,formaldehyde polymer, sodium salt. An effective amount of surfactantmust be incorporated into the formulation to provide sufficientdispersant activity when applied to the animal. Preferred non-ionicsurfactants are alkyl polysaccharides; alkyl phenol ethoxylates. Apreferred alkyl phenol ethoxylate is nonyl phenol ethoxylate.

Other ingredients may be suitably included, for example, wetting agents,thickeners, humectants, preservatives, buffers, anti-foaming agents,diluents, excipients, adjuvants, and/or carriers. Actives which have animmediate effect (ie “knock down”); dyes (scourable, water soluble);antioxidants or UV stabilizers (eg oxybenzone); and thixatropic agentsmay also be added. A preferred humectant is polyethylene glycol.

Thus, in a third aspect, the present invention provides a method forformulating a topically acceptable aqueous pour-on formulation adaptedfor localised external application to an animal, which method comprisesforming a first component by mixing a humectant and non-ionic surfactantuntil homogenous; adding water and mixing until homogenous; addingbuffer and anionic surfactant; adding insect growth regulator (IGR);forming a second component by mixing humectant and thickener; andcombining said first and second components.

Suitably, the first and second components are diluted to a desired andfinal volume.

In addition, suitably, the IGR is milled to form a particle size ofbetween about 2 to about 5 μm.

Suitable ranges for the ingredients are as follows: a) Active 5-50 g/Lb) Surfactants (non-ionic) 10-100 g/L c) Surfactants (anionic) 1-20 g/Ld) Wetting Agent 1-20 g/L e) Thickener 3-10 g/L

The “normal” ratio of the above would be a) :b) :c) :d) :e)=5:6:1:1:1. Amore general description of the ratio would beactive:surfactants/wetting agents/thickeners=1:2. These ratios would notbe expected to vary significantly with type of active or surfactants.The most effective ratio is that of the most preferred formulation whichhas been “balanced” to optimise all of the above. The optimum pH forthis formulation is in the range pH 5-9.

A particularly preferred formulation using the ranges of concentrationsabove would include diflubenzuron as the active; nonyl phenolethoxylate, alkylated naphthalene sulfonate, formaldehyde polymer,sodium salt, as the mixture of surfactants; sodium lauryl sulfate as awetting agent and Xanthan gum as a thickener or suspending agent.

Suitably, pour-on formulations include a colouring agent to enable theuser to visually monitor the application of the formulation to theanimal. The nature of the coloring agent is unimportant and a widevariety of suitable dyes and pigments will be known to the skilledperson.

Suitably, the ingredients are formulated as follows: (a) half of thepropylene glycol and non-ionic surfactant mixed in a mixing vessel untilhomogeneous. Water is then added and mixed until homogeneous. This isfollowed by buffer and anionic surfactant. Typically, anti-foam is thenadded and the mixture stirred. (b) The active ingredient is then addedand mixed until homogeneous. (c) The second half of the propylene glycolis mixed with the Xanthan gum and then added and again, the mixturestirred well until thorough mixing has occurred. The final volume isthen adjusted with water if necessary.

The pour-on formulation may be formulated for application by a spraytechnique, for example, as an aerosol using a liquid or gas aspropellent.

Depending on the efficacy of the particular active agent used, theformulation will generally contain from about 5 to about 50 g/L of theactive agent.

The external parasites which may be treated in accordance with thisinvention include ticks, fleas, flies (for example, sheep blow fly,buffalo fly, nuisance fly), lice (for example, cattle and sheep lice)and mites (for example, sheep mites). The insects and parasitesmentioned are indicative only, and numerous other insects and parasitescan be treated by the method of the present invention. Suitably, thecompositions and method of this invention may be used to treat the sheepbody louse which is classified as follows: Order—Phthiraptera, SubOrder—Mallophaga, Family—Trichodectidae, Genus—Damalinia (Bovicola,Tricholdectes), Species—Bovicola ovis (Schrank).

The animal is preferably a mammal, and may be selected from sheep,cattle, deer, goats, pigs, dogs, and cats. The animal may also be abird.

BEST AND OTHER MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments will now be described by way of non-limitingexamples.

EXAMPLE 1

TABLE 1 Diflubenzuron Sheep Lice Pour-on (25 g/L) Component Use (g/L)Diflubenzuron Active Ingredient 25.00 Nonyl phenyl ethoxylate (eg. TericNon ionic 30.00 GN15) Alkylated naphthalene sulfonate, Anionic 3.00formaldehyde polymer, Sodium salt (eg. surfactant Morwet D425) Sodiumlauryl sulphate BP (eg. Empicol Wetting agent 5.00 LZVD) Xanthan Gum USP(eg. Keltrol F) Thickener 5.10 Propylene Glycol USP Humectant 60.001,2-Benzisothiazoline-3-one (20% w/w) Preservative 1.00 in aqueousdipropylene gycol Solution (eg. Proxel GXL) Simethicone USP (eg.Antifoam A) Antifoam 1.00 Citric Acid (Anhydrous BP) Buffer  1.01 or qsDisodium hydrogen phosphate- Buffer 13.30 or qs Anhydrous Food GradeDeionised Water Diluent qs to 1 L

EXAMPLE 2 Details of Trial

Target Pest

Order—Phthiraptera, Sub Order—Mallophaga, Family—Trichodectidae,Genus—Damalinia (Bovicola, Trichodectes), Species—Bovicola ovis(Schrank) and Common name—Sheep body louse.

Test Animals

The sheep used in this study were a uniform line of Merino wethersheavily infected with lice.

The method requires examination of twenty partings each 10 cm long,along two contours on the left and right sides covering the wool growingregions of the animal. At each of the 40 recorded sites all live adultlice are counted. Site counts are summed to give a total count for theanimal.

Assessing lice populations in this manner also allows the production ofa map, showing how the lice are distributed over the body of the tracersheep.

TABLE 2 Treatment details Active (mg) Treatment per sheep Conc (g/L)Sheep Dose (mL) Diflubenzuron 500 25.0 5 20 Diflubenzuron 250 12.5 5 20

Test Treatments

Within 24 hours of shearing, treatments were applied as a single stripealong the backline of the sheep. The dose rate applied was based on 20mL of treatment per animal which is based on all test animals being inthe 30.1-55 kg weight range.

The delivery apparatus for each formulation was a commercial applicator,set to deliver 1×20 mL doses to the sheep backline. The gun wascalibrated using a volumetric cylinder and checked twice before and onceafter treatment.

To avoid the possibility of rain complicating the post treatmentsituation the sheep were kept in pens for a minimum of 48 hours. Then onthe morning of the 25 th day of the trial, they were placed into theirpaddocks.

Lice assessments were made on all sheep 2, 5, 10 and 20 weeks aftertreatment.

EXAMPLE 3

Effect of Diflubenzuron Formulations on Concentrations of Sheep Lice[Group Arithmetic Lice Counts (Standard Deviations)]

TABLE 3 Mean Lice Counts Diflubenzuron Weeks after treatment (g/L) 0 2 510 15 20 25.0 120.6 17.2 4.4 1.4 1.0 0.0  (74.2) (9.0) (7.7)  (2.6)(1.4) (0.0) 12.5 161.8  6.8 1.8 0.4 0.0 0.0 (124.7) (2.9) (2.50) (0.9)(0.0) (0.0)

TABLE 4 Field Efficacy (Control of sheep lice) DiflubenzuronConcentration is 25 g/L Pre treat- ment % Lice reduction mean after:Trial lice 6 12 20 No Location Animal Used count weeks weeks weeks 1Uraila, 1309 fine 156 98.1 98.7 100 N.S.W. wool merinos 2 Guyra, 2000super 41 100 100 100 N.S.W. fine wool 3 Crookwell, 680 medium 242 91.399.6 100 N.S.W. fine wool merinos 4 Lucindale, 1094 strong 35 99.8 100100 N.S.W wool merinos 5 Coonalpyn, 1101 strong 142 99.6 100 100 S.A.wool merinos 6 Lismore, 812 super 51 99.5 100 100 Vic fine merinos

EXAMPLE 4 Efficacy Trial

Effect of diflubenzuron in 12.5 and 25.0 g/L pour-on formulations(corrected lice counts) [Results of Table 3 converted to % licereduction]

TABLE 5 Diflubenzuron % Lice reduction after: (g/L) 2 weeks 5 weeks 10weeks 15 weeks 20 weeks 25.0 69.6 83.4 94.8 96.4 100.0 12.5 91.0 94.998.9 100.0 100.0

EXAMPLE 5 Results of Wetting Trial

TABLE 6 Group mean lice counts Group Days Post Treatment No TreatmentWetting 0 22 44 84 142 1 25 g/L No 92.0 2.5 0.5 0.3 0.2 diflubenzuronwetting 2 25 g/L 25 mm rain 105.5 5.8 0.3 0.2 0.0 diflubenzuron beforetreatment 3 25 g/L 25 mm 110.0 0.7 1.2 0.3 0.0 diflubenzuron rain aftertreatment 4 Untreated 25 mm 92.7 13.5 10.5 2.2 17.0 rain beforetreatment 5 Untreated No 106.3 15.7 7.0 2.0 17.5 wetting

TABLE 7 Effect of rain on diflubenzuron pour-on (percent reductions)Group Days Post Treatment No Treatment Wetting 22 44 84 142 1 25 g/L Nowetting 81.6 86.8 82.7 98.7 diflubenzuron 2 25 g/L 25 mm rain 62.8 95.789.9 100.0 diflubenzuron before treatment 3 25 g/L 25 mm rain 95.7 83.685.6 100.0 diflubenzuron after treatment 4 Untreated No wetting 1.4−72.0 −26.1 −11.4

Note that these reductions have been calculated using the mean licecounts of Group 5, that is, the sheep kept dry. The following formulawas used to calculate percent lice reductions.

% reduction=[1-(Untreated PT/Treated PT×Treated Time T/Untreated TimeT)]1×100,

where PT is average lice number, and T is the average lice number attime post treatment.

EXAMPLE 6 Pen Efficacy Trial (Control of Cattle Lice)

Efficacy of 25 g/L diflubenzuron pour-on against cattle lice.

TABLE 8 Pre Dose treatment % Lice reduction after: Group Rate mean lice14 28 42 60 72 84 No mg/kg counts days days days days days days 1 5 9957.7 52.5 94.8 92.2 95.7 87.9 2 10 89 68.7 62.9 96.2 99.3 98.1 100 3 1597 81.9 62.7 94.6 95.1 99.0 100

EXAMPLE 7 Field Efficacy (Prevention of Strike by Sheep Blowfly)

Fourteen field efficacy trials were carried out under a range ofclimatic conditions throughout the eastern states of Australia. The datagenerated showed that the 25 g/L diflubenzuron formulation gave a highlevel of protection against body and crutch strike. Less than 0.1% ofthe 2316 sheep treated suffered body strike and 0.35% crutch strike. Flypressure was measured using 2 flytraps within each paddock housing thetreated sheep.

EXAMPLE 8 Pen Efficacy Trials (Larval Implant Studies to DemonstrateEfficacy Against Strike by Sheep Blowfly, Lucilia Cuprina)

Pen studies have demonstrated that the aqueous product, when applied asa spray-on along the backline of long wooled sheep, is efficaciousagainst the larval stages of the sheep blowfly, Lucilia cuprina.

EXAMPLE 9 Tissue Residues

Tissue residue studies were carried out following application of theaqueous pour-on to both sheep and cattle (Reference is made to page 1,lines 34 and 35 where it is mentioned that treatment with non aqueouspour-on formulations can lead to high tissue residues in animals treatedwith these formulations.)

TABLE 9 Sheep: Diflubenzuron residues after treating at a dose rate of20 mg/kg Days post Level of diflubenzuron residues in tissues (mg/kg)treatment Muscle Liver Kidney peri-renal fat Inguinal fat 1 <LOQ <LOQ<LOQ 0.03 max 0.02 max 3 <LOQ <LOQ <LOQ 0.02 max 0.04 max 7 <LOQ <LOQ<LOQ 0.02 max 0.03 max 14 <LOQ <LOQ <LOQ <LOQ 0.02 max 21 <LOQ <LOQ <LOQ<LOQ 0.05 max 42 <LOQ <LOQ <LOQ <LOQ <LOQ Note: Limit of quantitation(LOQ) = 0.02 mg/kg

TABLE 10 Cattle: Diflubenzuron residues after treating at a dose rate of15 mg/kg Days post Level of diflubenzuron residues in fat tissues(mg/kg) treatment Peri-renal fat Inguinal fat 1 0.17 <LOQ 3 0.09 <LOQ 7<LOQ <LOQ 14 <LOQ <LOQ Note: 1. Limit of quantitation (LOQ) = 0.02 mg/kg2. Muscle, liver and kidney tissues have not been tested as thediflubenzuron will preferentially go into the fat tissues.

EXAMPLE 10 Comparative Stability of Formulations Containing Nominally 25g/L Diflubenzuron and 25g/L Triflumuron.

TABLE 11 Stability of aqueous triflumuron pour-on after 6 weeksaccelerated testing Storage Temp. Appearance pH Viscosity Cps Assay g/L 4° C. Purple suspension 7.59 922 24.0 30° C. Purple suspension 7.53 80024.2 40° C. Purple suspension 7.48 772 23.6 50° C. Purple suspension7.44 818 24.1

TABLE 12 Stability of aqueous diflubenzuron pour-on after 16 weeksaccelerated testing Viscosity Storage Temp Appearance pH Cps Assay g/L 4° C. Purple suspension 7.56 835 25.1 30° Purple suspension 7.48 82125.3 40° C. Purple suspension 7.48 855 26.0 50° C. Purple suspension7.50 913 26.0

SUMMARY

Efficacy data shows that rainfall pre or post treatment does not affectthe efficacy of the formulation i.e. the product will be rainfast.

Insect growth regulators act by preventing the formulation of chitinduring the insects moulting phase. They prevent the development ofimmature lice present in the fleece at the time of application and thosewhich hatch from eggs in the following weeks. Adult lice die outnaturally over a few weeks (can take up to 14).

The surprisingly quick knockdown effect (95.7% reduction in lice) of theformulation after post treatment rainfall (22 days) is shown. Four outof six sheep in the group had no lice present. This demonstrates thatthe surfactants do help to spread the formulation when the product isapplied in the wet.

The foregoing describes only some embodiments of the present inventionand modifications obvious to those skilled in the art can be madethereto without departing from the scope of the invention.

INDUSTRIAL APPLICABILITY

It should be clear that the present invention will find wideapplicability in the agricultural and veterinary science areas.

What is claimed is:
 1. A topically acceptable aqueous pour-onformulation adapted for localized external application to an animal,which formulation consists essentially of an effective amount of waterinsoluble insect growth regulator (IGR), a suspending agent, an anionicsurfactant, a non-ionic surfactant or mixtures thereof, and an aqueouscarrier, wherein said IGR is selected from the group consisting ofdiflubenzuron, triflumuron, fluazurin and methoprene, said suspendingagent is selected from the group consisting of xanthan gum, colloidalsilica, bentonite, polyvinylpyrrolidone, cellulose and alginates, andsaid surfactant or surfactants are selected from the group consisting ofalkylated naphthalene sulfonate, formaldehyde polymer sodium salt, alkylpolysachcharides, and alkyl phenol ethoxylates, and optionally wettingagents, thickeners, humectants, preservatives, buffers, anti-foamingagents, diluents, excipients, adjuvants, and/or carriers, dyes, andantioxidants.
 2. The formulation according to claim 1 wherein thesuspending agent is xanthan gum.
 3. The formulation according to claim 1wherein the humectant is polyethylene glycol.
 4. The formulationaccording to claim 3 wherein the IGR is about 5-50 g/L; the anionicsurfactant is about 1-20 g/L; the non-ionic surfactant is about 10-100g/L; the wetting agent is about 1-20 g/L and the thickener is about 3-10g/L.
 5. A method for controlling external parasites which methodincludes externally applying to an animal an effective amount of anaqueous pour-on formulation adaped for localized external application toan animal, which formulation consists essentially of an effective amountof water insoluble insect growth regulator (IGR), a suspending agent, ananionic surfactant, a non-ionic surfactant or mixtures thereof, and anaqueous carrier, wherein said IGR is selected from the group consistingof diflubenzuron, triflumuron, fluazurin and methoprene, said suspendingagent is selected from the group consisting of xanthan gum, colloidalsilica, bentonite, polyvinylpyrrolidone, cellulose and alginates, andsaid surfactant or surfactants are selected from the group consisting ofalkylated naphthalene sulfonate, formaldehyde polymer sodium salt, alkylpolysachcharides, and alkyl phenol ethoxylates, and optionally wettingagents, thickeners, humectants, preservatives, buffers, anti-foamingagents, diluents, excipients, adjuvants, and/or carriers, dyes,antioxidants, and a propellant.
 6. The method according to claim 5wherein the formulation is applied as a spray technique.
 7. The methodaccording to claim 5 wherein said propellant is a liquid or gas.
 8. Themethod according to claim 5 wherein the IGR is from about 5 to about 50g/L.
 9. The method according to claim 5 wherein the parasites includeticks, fleas, flies, lice and mites.
 10. The method according to claim 9wherein the flies may be sheep blow fly, buffalo fly or nuisance fly;the lice may be cattle or sheep lice; and the mites are sheep mites. 11.A method for formulating a topically acceptable aqueous pour-onformulation according to claim 1, which method consists essentially offorming a first component by mixing said humectant and said non-ionicsurfactant until homogenous; adding water and mixing until homogenous,adding said buffer and said anionic surfactant; adding said insectgrowth regulator (IGR); forming a second component by mixing saidhumectant and said thickener; and combining said first and said secondcomponents.
 12. The method according to claim 11 wherein the combinedfirst and second components are diluted to a desired final volume. 13.The method according to claim 11 wherein the IGR is milled to form aparticle size of between about 2 to about 5 μm.
 14. A topicallyacceptable aqueous pour-on formulation adapted for localized externalapplication to an animal, which formulation comprises: a) an affectiveamount of diflubenzuron wherein said diflubenzuron is present in amountfrom 5-50 g/L; b) Xanthan gum wherein said Xanthan gum is present inamount from 3-10 g/L; c) a surfactant or mixture of surfactants selectedfrom nonylphenolethoxylate; alkylated naphthalene sulfonate,formaldehyde polymer or sodium salt, wherein said surfactant or mixtureof surfactants are present in amount from 10-100 g/L; d) sodium laurylsulfate, wherein said sodium lauryl sulfate is present in amount from1-20 g/L; and e) an aqueous carrier.